Perfect absorber based on symmetric square silicon grating with polarization and angular stability using particle swarm optimization algorithm

In this study, we introduce and simulate a symmetric square Si (silicon) grating absorber optimized using particle swarm optimization (PSO). To carry out the simulation of the absorption spectrum, we utilize the three dimensional (3D) finite-difference time-domain (FDTD) method. The unit cells are made up of a combination of silicon square grating, gold, and quartz. The physical absorption mechanism is that a strong light response is caused by surface plasmon resonance. We have optimized geometric parameters to get the optimal output of the designed plasmonic absorber. In the wavelength ranging from 4000 to 6000 nm, we obtain a narrowband absorption peak with perfect absorption of over 99.9%. Additionally, the proposed absorber's performance is analyzed concerning incident angle and polarization, which shows good polarization and incident angle stability. Through manipulating the geometrical parameters, the structure exhibits a high sensitivity of 1606 nm.RIU⁻¹ and figure of merit (FOM) of 30. Due to the high sensing performance, this absorber can be broadly used in spectral sensing, biosensing, photon detection, and other fields.